A nonaqueous electrolyte battery takes advantage of excellent characteristics at high voltage for use in various applications.
Stainless steel is generally used as the positive electrode case material for the nonaqueous electrolyte battery. High voltage batteries with 3.5 V or more per cell suffer from the problem that when stored for long periods, a portion of the positive electrode case becomes corroded and leaks liquid. Corrosion of the positive electrode case is caused by ionization of iron in the stainless steel case and dissolution of iron ions in the electrolyte. Continuation of the dissolution reaction leads finally to a corrosion hole in the positive electrode case and electrolyte leakage.
A primary lithium battery using an aluminum case was developed to prevent case corrosion. Since the dissolution voltage of aluminum is higher than that of stainless steel, positive electrode case corrosion can be prevented using aluminum.
However, to obtain high output voltage a large area spiral electrode unit is used. In the case of charge collection in a nonaqueous electrolyte battery by the positive electrode active material on the outermost winding of the spiral electrode unit contacting the aluminum positive electrode case, performance problems arise from increase in internal resistance as the electrical contact degrades. To prevent this problem, a complex structure was necessary provided a special tab-lead on the positive electrode of the spiral electrode unit for connection with the positive electrode case.
The present invention was developed for the purpose of solving problems such as those described above. It is thus a primary object of the present invention to provide a highly corrosion resistant, light weight nonaqueous electrolyte battery with a simple electrical connection scheme and excellent discharge capacity and cycling characteristics.